Oil or tar sands are a source of bitumen, which can be reformed into a synthetic crude or syncrude. At present a large amount of hydrocarbon is recovered through surface mining. To obtain syncrude, the hydrocarbons must be first separated from the sand base in which it is found. This sand based material includes sands, clays, silts, minerals and other materials. The most common separation first step used on surface mined tar sands is the hot water separation process which uses hot water to separate out the hydrocarbons. However, the separation is not perfect and a water based waste liquid is produced as a by-product which may include small amounts of hydrocarbon, heavy metals, and other waste materials. The oil producers currently deal with what they call Fresh Fine Tailings (FFT) and Mature Fine Tailings (MFT); the distinction between the two being that MFT are derived from FFT after allowing sand to settle out over a period of typically 3 years. MFT are mostly a stable colloidal mixture of water and clay, and other materials, and is collected in onsite reservoirs called tailings ponds.
Oil extraction has been carried out for many years on the vast reserves of oil that exists in Alberta, Canada. It is estimated that 750,000,000 m3 of MFT have been produced. Some estimates show that 550 km2 of land has been disturbed by surface mining yet less than 1% of this area has been certified as reclaimed. A 100,000 bbl/day production facility produces 50,000 tonnes per day of FFT, which is equivalent to approximately 33,500 m3 of FFT per day.
The FFT and MFT present three environmental and economic issues: water management, sterilization of potentially productive ore, and delays in reclamation. Although concentrations vary, MFT/FFT can typically comprise 50 to 70% water. This high water content forms, in combination with the naturally occurring clays, a thixotropic liquid. This liquid is quite stable and persistent and has been historically collected in large holding ponds. Very little has been done to treat the MFT that has been created and so it continues to build up in ever larger holding ponds. As development of the tar sands accelerates and more and more production is brought on line, more and more MFT/FFT will be produced. What is desired is a way to deal with the MFT/FFT that has been and will be generated to permit land reclamation, release of captured water and provide access to the productive ore located beneath such ponds.
MFT/FFT represents a mixture of clays (Mite, and mainly kaolinite), water and residual bitumen resulting from the processing of oil sands. In some cases MFT may also be undergoing intrinsic biodegradation. The biodegradation process creates a frothy mixture, further compounding the difficulty in consolidating this material. It is estimated that between 40 and 200 years are required for these clays to sufficiently consolidate to allow for reclamation of tailings ponds. Such delays will result in unacceptably large volumes of MFT, and protracted periods of time before reclamation certification can take place unless a way to effect disposal and reclamation is found. The oil sands producers are required by a directive of the Energy Resources Conversation Board to treat their tailings to a bearing capacity of 5 kPa by 2012 and 10 kPa by 2015.
Applied electrical fields have been used to dewater soils for construction projects to improve bearing capacity. Electrophoresis has been used in many industries, such as the pharmaceutical industry and ceramics industry to produce high grade separations. Electrostriction has been used to create high density ceramics. In electrical resistance heating treatment at Fargo, N. Dak. (Smith et al., 2006)a, electrastrictive phenomenon has been observed in the application of an electric field to already consolidated clays where the applied electric field ranged between 0.46 to 0.8 volt/cm. Examples of applications of electrical fields in various circumstances can be found in the following prior patents. a Smith, G. J., J. von Flatten, and C. Thomas (2006) Monitoring Soil Consolidation during Electrical Resistivity Heating. Proceedings of the Fifth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, May 22-25, 2006, Monterey, Calif.,                U.S. Pat. No. 3,962,069        U.S. Pat. No. 4,107,026        U.S. Pat. No. 4,110,189        U.S. Pat. No. 4,170,529        U.S. Pat. No. 4,282,103        U.S. Pat. No. 4,501,648        U.S. Pat. No. 4,960,524        U.S. Pat. No. 5,171,409        U.S. Pat. No. 6,596,142        
The application of electrical current to oil sands tailings has also been tried, as shown in U.S. Pat. No. 4,501,648. However, this teaches a small device with a tracked moving immersed electrode onto which is deposited clay solids. The electrode is moved out of contact with the liquid and then the solids are scraped off the electrode. A chemical pre-treatment step is required to achieve the desired deposition rate on the immersed electrode. While interesting, this invention is too small to be practical for MFT/FFT treatment and requires a chemical pre-treatment step which adds to the cost.
The application of electrical fields to treat small-scale clay deposits may not require efficient use of energy. However, on a large scale, the application of an electrical current requiring high power consumption or requiring an application of an electrical current over a long period of time may be prohibitively expensive or impossible to carry out due to the available resources. At remote sites, large-scale access to electrical power may be limited. Small variations in electrical current draws may have significant impact on costs and power requirements when dealing with millions of square meters of MFT and FFT.
What is desired is a way to deal with vast volumes of MFT/FFT that will need to be treated without excessive power expenditures. What is desired is a practical system for dealing with tailings efficiently and quickly. What is also desired is a way to extract water from large volumes of MFT/FFT which can be re-used for other purposes.